Transcript: We begin here with a stunning new image caught on a neighbor’s surveillance camera. A 71-year-old man shot while working in his lawn.

It is a chilling reminder of a city already in crisis. You can see the two suspects approach on bikes. One man then wrestling with the homeowner. Moments later, that homeowner is shot. And then you can see him trying to find help. Tonight, we’ve learned he’s in intensive care, that city in shock. And it comes after that stunning new number. 500 homicides, just this year.

ABC’s Alex Perez with the video from Chicago tonight.

Reporter: It takes just seconds. 71-year-old Frederico Laguardia, out watering his lawn, when two young men on bikes ride past him. What happened next, tonight, a cruel symbol of the gun violence plaguing Chicago. With Laguardia still standing there, one of the men returns, confronting the senior citizen. Wrestling him to the ground, shooting him and rifling through his pockets. Then getting back on his bike and riding off. Laguardia wounded, but able to stand, staggers across the lawn. Clutching his abdomen, he walks to a neighbor’s door. No answer. Laguardia sits on the steps and calls for help. It’s just absolutely ridiculous. I mean — you’re not even safe in your own yard.

Reporter: Tonight, the shooting of Frederico Laguardia, more proof of the violence gripping some Chicago neighborhoods. This is not an individual thing. It happened to all of our grandfathers. It happened to all of our fathers. It’s happened to all of Ou sons. Reporter: Nearly 3,000 shootings in Chicago just this year. 500 people killed in the wave of violence. 90 dead in August alone — the deadliest month in two decades. It’s not a police issue, it’s a society issue. You know, impoverished neighborhoods, people without hope do these kinds of things. You show me a man who doesn’t have hope, I’ll show you a man who’s willing to pick up a gun and do anything with it.

Reporter: And tonight, Federico Laguardia’s neighbors with this appeal to the parents of those young men on the bikes. If you can identify that’s your child on there, do the right thing before you get that knock on your door that your child has been arrested, because it’s coming. It’s coming. And Alex Perez is live in Chicago tonight. And Alex, you’ve reported extensively on the violence there, the efforts to bring it in check. And tonight, the victim’s family is with him? Reporter: That’s right, David. We talked to his wife, who tells us, he’s in the hospital, doing better, and in fair condition. Neighbors who live here tell us this shooting is just another sign of the crisis so many people in this city are facing. David?

No amount of political posturing can help a problem like this. There needs to be a change of heart.